CONCORD, N.H. — A New Hampshire man convicted of gunning down a Manchester police officer 40 years ago at age 15 has been granted parole.

Cleo Roy has been serving a 50-year sentence for shooting Officer Ralph Miller as the officer approached his house to investigate a noise complaint, which stemmed from a teenage drinking party Roy was holding in his parents’ absence.

Miller was 25 and a Navy veteran with one year on the force when he was shot and killed. He had a 3-year-old daughter, and his wife was pregnant with their second child. They had moved into a new home days before the shooting.

Roy, who pleaded guilty to second-degree murder, expressed remorse for the shooting. He last applied for parole in 2011. The state parole board denied it, noting his “atrocious” behavior during his first dozen years in prison outweighed leadership he showed in counseling convicts and helping prison officials maintain order.

Roy entered the state prison in 1976. He escaped during his first year there, which led to a transfer to the federal penitentiary in Marion, Illinois. There, he joined the white supremacist prison gang, the Aryan Brotherhood, and drew a federal racketeering conviction in connection with the killing of another inmate gang member in 1988. He told the board in 2011 after five years in an isolation cell at Marion, he walked away from the gangs.

On Tuesday, the board noted that since 2011, the 55-year-old Roy has been “disciplinary-free,” finished programs to help his job prospects and manage his finances, established strong family and community support, started family counseling, and notified the police in his proposed community of release. Roy will be under supervision of a parole officer who will assist in his transition to society.

Miller’s family and the Manchester Police Department did not support Roy’s release. Family members did not attend Tuesday’s hearing.

“This has been extremely difficult for them,” Senior Assistant Attorney General Jeffery Strelzin said Wednesday. “They don’t feel that the punishment fits the crime. But they respect the fact that parole board made the decision that they did, as do we.”